This application is based upon Japanese Patent Application No. 337559 of Heisei 10, filed Nov. 27, 1998, and its contents are incorporated herein by reference.
The present invention relates to a swivel control apparatus for a construction machine such as a crane or the like.
In a control system for swiveling, in the past, there is a mode (termed the xe2x80x9cneutral free modexe2x80x9d) in which the motor is rotated by the inertia of the swiveling body when the operating lever has been returned to neutral; and there is a mode (termed the xe2x80x9cneutral brake modexe2x80x9d) in which the rotation of the motor is stopped when the operating lever has been returned to neutral. It is desirable for the use of these modes to be separated according to the nature of the job, and for example in Japanese Patent Publication Serial No. 2,549,420 there is disclosed an apparatus with which either of these modes can be selected with one machine. With the apparatus of this publication, respective relief valves are provided to conduits connected to the input and output ports of the hydraulic motor, and a relationship between the amount of actuation of the operating lever and the relief pressures of the relief valves are made into patterns and established in advance for each of the neutral free and neutral brake modes. It is possible to control the driving of the swiveling body in correspondence with each of the neutral free/neutral brake modes by controlling the relief valves in accordance with these characteristics (patterns) of relief pressure.
The above described characteristics of the relief valves of the apparatus described in the above publication are set so that the amounts of change of the relief pressure become greater in accompaniment with increase of the actuation amount of the operating lever, and since the relief valve is controlled in accordance with these characteristics, even in the case that the operating lever is actuated for deceleration by exactly the same amount, according to the position from which the operating lever was actuated, the amounts of change of the relief pressures vary. In other words, although the relief pressures vary greatly in positions in which the slopes of the characteristics are large, the relief pressures vary hardly at all in positions in which the slopes of the characteristics are small. As a result great differences occur in the deceleration of the motor due to the position of the operating lever, even if the operating lever is operated for deceleration by exactly the same amount, and operation becomes difficult from the point of view of the operator.
Further, with the apparatus described in the above publication, a plurality of different relief characteristics are set for the relief valves according to the direction of actuation of the operating lever, the direction of rotation of the motor, and whichever of the neutral free/neutral brake modes is established, and for this reason the control algorithm becomes complicated. In the above publication an apparatus is disclosed in which one relief valve is provided in order to simplify the control algorithm, but in this case the problem arises that, even in the neutral free mode, a large braking pressure is generated due to the actuation region of deceleration actuation of the operating lever.
The objective of this invention is to provide a swivel control apparatus which can most suitably realize the neutral free mode and the neutral brake mode by a simple construction.
In order to attain the above object, a swivel control apparatus according to the present invention , comprises: a hydraulic pump; a hydraulic motor for swiveling which is driven by hydraulic oil emitted from the hydraulic pump; a control valve which controls a flow of hydraulic oil which is supplied from the hydraulic pump to the hydraulic motor for swiveling, and at a neutral position of the control valve cuts off from one another a pair of ports which communicate to input and output ports of the hydraulic motor; a valve device which communicates and cuts off from one another a pair of conduits which are respectively connected to the input and output ports of the hydraulic motor for swiveling; a pressure detection device which detects respective pressures in the two conduits and outputs pressure signals; a rotational speed detection device which detects a physical quantity based upon a rotational speed of the hydraulic motor for swiveling and outputs a rotational speed signal; a mode selection device which selects a neutral brake mode and a neutral free mode; and a control device which controls driving of the valve device so as to cut off the two conduits from one another when the neutral brake mode is selected, and so as to communicate the two conduits based upon the pressure signals and the rotational speed signal when the neutral free mode is selected.
In this swivel control, it is preferred that the control device calculates a direction of action of hydraulic oil upon the hydraulic motor based upon the pressure signals, calculates a rotational direction of the hydraulic motor based upon the rotational speed signal, and controls the driving of the valve device so as to communicate the two conduits when the neutral free mode is selected and the calculated direction of action of hydraulic oil upon the hydraulic motor and the rotational direction of the hydraulic motor are different. In this case, it is preferred that the control device calculates a target flow amount based upon the rotational speed signal and controls the driving of the valve device so that the target flow amount flows from one of the conduits to the other of the conduits. In addition, it is preferred that a deceleration ratio setting device which sets a deceleration ratio for the hydraulic motor for swiveling is further provided, and the control device calculates the target flow amount based upon a set value from the deceleration ratio setting device. Or it is preferred that the control device controls the driving of the valve device based upon a conversion table that is predetermined to obtain a value of a control signal for the valve device based upon the target flow amount. Or it is preferred that the target flow amount is assumed as a value for a flow amount passing through an orifice, a differential pressure between the two conduits detected by the pressure detection device is assumed as a value for a differential pressure of orifice, and the control device calculates an opening amount of orifice by substituting the assumed values into an equation based upon the orifice equation, and controls the driving of the valve device based upon a control signal corresponding to the calculated opening amount of orifice.
It is preferred that the valve device described above is an electromagnetic proportional valve and is controlled so as to be closed when the neutral brake mode is selected and so as to be opened with a predetermined opening area when the neutral free mode is selected.
A hydraulic swiveling type of crane according to the present invention comprises: a traveling body; a swiveling body that is mounted upon the traveling body to be able to swing; and the above described swivel control apparatus that controls swiveling of the swiveling body.
As described above, in the present invention, the valve apparatus which communicates together and cuts off from one another a pair of conduits which are respectively connected to the input and output ports of the hydraulic motor for swiveling is provided, in the neutral brake mode the two conduits are cut off from one another, and in the neutral free mode the two conduits are communicated based upon the pressure signals and the rotational speed signal, therefore it is possible to realize a suitable one of the neutral free/neutral brake states without any dependence upon the actuation position of the operating lever. The control algorithm becomes simplified compared with one in which each of the neutral free/neutral brake states is realized according to the predetermined patterns. In particular, since the target flow amount that is calculated based upon the rotational speed signal flows from one of the conduits to the other of the conduits, the speed control of the swiveling body can be performed accurately. Furthermore, since it is possible to set the deceleration ratio of the hydraulic motor for swiveling, therefore in the neutral free mode it is possible to alter the deceleration of the swiveling body to any value, and the convenience of use is enhanced.
Furthermore, since the conversion table that is predetermined to obtain a value of a control signal for the valve device based upon the target flow amount is used, the control can be implemented easily and the high speed of control can be achieved. And various types of empirical or experimental values can be used for the conversion table. On the other hand, in case that the equation based upon the orifice equation is used, the amount of memory where the conversion table is stored can be reduced. In addition, the target opening amount is calculated in consideration of not only the target flow amount but also the differential pressure, the target flow amount can be controlled with high accuracy. Also, the hydraulic swiveling type of crane can have above advantages.